The present invention relates generally to a steam power plant having a multistage turbine which is fed by a nuclear reactor of the boiling reactor type.
A power plant of this type typically operates without a superheater for the high-pressure steam. Accordingly, supersaturated wet steam will develop due to the lack of a superheater. The wet steam occurs primarily in the lower pressure stages, in other words downstream of the high-pressure stage. Such hot, wet steam will have a highly corrosive effect on iron surfaces, especially in the temperature range of 150.degree. C. to 180.degree. C. The highly corrosive effect is due to the fact that the water which precipitates from the wet steam and is deposited on the surfaces of the steam conduits, has a very low oxygen content in this specific temperature range. Therefore, a protective oxide film can not form on the surfaces with the result that corrosion can and will spread throughout the steam conduits.
The water film within the steam conduits will have a low content of oxygen even though the oxygen content of the steam inside the reactor can be high due to radiolysis. This phenomenon is caused by the fact that the oxygen distribution between the water and the steam will greatly favor the steam phase in this specific temperature range. It is for this reason that the problem of corrosion can not be solved by the admission of pure oxygen to the steam.
To overcome the problems of the prior art, the invention includes the admixture of hydrogen peroxide to the steam, to be accomplished most advantageously by blowing hydrogen peroxide in a suitably dissolved state into the flow of steam. The hydrogen peroxide will thus dissolve in water droplets of the steam. Computations indicate that the hydrogen peroxide will remain effective for a period of time that is sufficient to build up and maintain an oxide film at the steel surfaces that are subjected to the hot and wet steam.
The use of hydrogen peroxide as an agent for corrosion prevention in conventional steam power plants is known per se but only as an additive to the condensation product and to the feed water. There is hardly any danger of corrosion in the steam section of such plants because the plants operate with superheated steam entirely at a sufficiently high temperature level. On the other hand, there is no need for an admixture of additional oxygen to the condensation product and to the feed water of a nuclear power plant because the oxygen, which is produced by the radiolysis in the reactor, can supply the condensation product and feed water with the desired oxygen content in the water.
The admixture of hydrogen peroxide is necessary in sections where wet, hot steam is present, in other words immediately after the high-pressure stage of the turbine. In order to attain a proper distribution of the additive, it will be expedient to admix it in front of the high-pressure stage.